1. Field of the Invention
The present invention relates to an image data processing apparatus for a digital video tape recorder (hereinafter, referred to as "digital VTR") in which image data as much as possible can be reproduced from a recording medium in order that image quality can be further improved, and a method for processing image data therein.
2. Description of the Prior Art
Generally, a digital VTR for recording and reproducing image data by using a well-known digital signal processing method in the art has variety and many advantages in function, but has a problem that an amount of data to be processed therein is much larger as compared to an analog VTR widely-known for home use.
Accordingly, since a digital VTR for home use has to be able to use a magnetic tape for an analog VTR, which has been widely used at home, to record and reproduce image data on the magnetic tape, the image data has to be compressed to reduce the amount of the image data to be processed.
Also, when image data are recorded and reproduced, errors occur inevitably. If the image data are recorded and reproduced by compression, image damage due to the errors is serious, compared to the recording and reproducing of the image data without compression. Errors generated during reproducing of image data should be reduced as much as possible and such a digital VTR can reproduce image data at high speed as with the analog VTR.
The two subjects as described above can be solved by an error correction coding (hereinafter, referred to as "ECC") method and a tape formatting method.
In the ECC method, in order to effectively correct a random error and a burst error generated during recording or reproducing operation, an outer ECC process and an inner ECC process are performed so that a logic product code is generated, and then an interleaving process is performed using the logic product code. Accordingly, the random error can be corrected by the inner and outer ECC processes, and the burst error is converted into a random error that can be corrected.
Since the interleaving method is related to a tape format in which image data are recorded on a magnetic tape having a predetermined pattern, the tape format has an important effect upon image quality when a reproducing operation is performed with a change of speed in a digital VTR.
FIG. 1 is a plane view of a tape showing a scanning path of a head during reproducing operation of double speed in a tape format in which image data of one frame are divided and recorded in two tracks, and FIG. 2 is a plane view of a tape showing a scanning path of a head during reproducing operation at three times speed.
In FIGS. 1 and 2, portions indicated by broken lines are ones to be scanned by the head and portions indicated by hatching are ones to have been reproduced by the head. A part of image data reproduced from only the hatched portions of each track is useful as correct data.
When the reproducing operation is performed at a normal speed, image data recorded in all portions of each track are reproduced, but when the reproducing operation is performed at a high speed, image data recorded in only a portion of each track are reproduced as shown in the hatched portion of FIG. 2. As described above, reproducing of a part of the image data has a bad influence upon image quality.
Particularly, if image data reproduced from only a part of each track are reconstructed in the home digital VTR capable of compressing and reproducing of image data, loss of image data is substantially increased as compared to reproducing of image data without compression. For this reason, even though the reproducing operation at high speed is performed using the interleaving process and the tape formatting process, it has to be considered that image data as much as possible can be reproduced from a recording medium. Also, even in a broadcasting VTR in which image data are not compressed to be recorded and reproduced, the image data are recorded on several tracks of a magnetic tape in random so that good image quality can be obtained during reproducing operation at high speed.
However, in the home VTR in which image data are compressed to be recorded and reproduced, the image data are divided into a plurality of segments to be recorded and reproduced. Then, the image data are compressed substantially by recording in the middle portion of a recording tape, and the recorded image data are reproduced from the middle portion during the reproducing operation at high speed so that data reproduction at high speed can be performed.
Generally, an ECC method is used to correct errors generated during the reproducing operation, and preferable the tape formatting method of the conventional methods as described above is that image data are transformed to a logic product code to be recorded on a recording tape at random or in a segment. In this method, outer codes not to be used in the reproducing operation are encoded by an outer encoding process to be transformed to additional information. The additional information are encoded by an inner encoding process to be transformed to further additional information. The information formed thus are recorded on the recording tape at random or in a segment.
Therefore, for image data reproduced during reproducing operation at high speed, outer decoding data necessary for performing the outer decoding process are reproduced together with the image data. If inner decoding data necessary for performing the inner decoding process in place of the outer decoding data are reproduced, image quality can be further improved.
In FIG. 6, a conventional tape format of data in two fields of one frame are respectively recorded in two tracks T1 and T2 is shown. An example of the data format to be recorded in accordance with the conventional tape format is illustrated in FIGS. 3 to 5.
As seen above, when the reproducing operation at high speed is performed since data recorded in the upper and bottom portions of each track except for the middle portion of each track are not reproduced and the reproducing head scans along two tracks simultaneously, the reproduced data amplified by an amplifying are not accurately reproduced.